docs: def setTransducer(self, edfsignal, transducer):
          """
          Sets the transducer of signal edfsignal
  
          :param edfsignal: int
          :param transducer: str
  
          Notes
          -----
          This function is optional for every signal and can be called only after opening a file in writemode and before the first sample write action.
          """
          if (edfsignal < 0 or edfsignal > self.n_channels):
              raise ChannelDoesNotExist(edfsignal)
          self.channels[edfsignal]['transducer'] = transducer
          self.update_header()